DATAJPA-494 - Fix template.mf to make sure auditing can be used on OSGi.

template.mf now contains an explicit Import-Package directive to make sure the relevant packages for the auditing functionality can be resolved in an OSGi environment. This hadn't been the case before as we don't explicitly refer to some classes necessary (mostly to prevent class loading errors in IDEs). The explicit declarations make sure the relevant Import-Package declarations are added even if Bundlor doesn't find any types that would explicitly require the imports.

JpaAuditingRegistrar now also explicitly hints to the class not being visible in case of auditing setup errors.

Original pull request: #62.